Static Loading Experiments Research Articles

Shear Performance of RC Beams Strengthened with High-Performance Fibre-Reinforced Concrete (HPFRC) Under Static and Fatigue Loading.

This study experimentally assessed the shear performance of reinforced concrete (RC) beams strengthened with U-shaped High-Performance Fibre-Reinforced Concrete (HPFRC) under static and fatigue loading. Key parameters included HPFRC jacket thickness and beam shear span-depth (a/d) ratio. Five beams were tested under static loads to determine ultimate shear strengths, followed by fatigue tests on identical beams at 30-70% of ultimate shear strengths at 4 Hz. In static loading experiments, all the HPFRC jacketing proved effective, increasing the shear strength of RC beams by 95% to 130%. Although the strengthening system did not change the failure mode of the beams, the strengthened beams exhibited pseudo-ductile behaviour. As the a/d increased, the shear enhancement capability of the HPFRC jackets decreased. In fatigue loading experiments, all the HPFRC systems improved the fatigue life of RC beams. Specifically, in beams with an a/d ratio of 2.0, the fatigue life was extended from 75 cycles to a maximum of 951 cycles, while in beams with an a/d ratio of 3.5, it increased from 12,525 cycles to 48,786 cycles. In addition, a predictive model has been developed for the fatigue life of HPFRC/UHPFRC shear-strengthened beams, utilising the maximum fatigue load and the design's ultimate shear strength under static loading conditions.

Soft elasticity enabled adhesion enhancement of liquid crystal elastomers on rough surfaces

The fabrication of pressure-sensitive adhesives (PSA) using liquid crystal elastomers (LCE) that are tolerant to substrate roughness is explored in this work. Traditional soft adhesives are designed by maintaining a balance between their cohesive strength and compliance. However, rough surfaces can significantly affect the adhesion strength of PSAs. Lowering the stiffness of the adhesive by reducing the cross-linking density or using additives can improve contact on rough surfaces. But this also decreases the cohesive strength and affects the overall performance of the adhesive. Additive-free LCE-based adhesives are shown to overcome these challenges due to their unique properties. Soft elasticity of LCE and low cross-link density contribute to their high compliance, while moderate cross-linking provides finite strength. The effect of contact time and substrate roughness on the adhesive performance is evaluated using probe-tack, indentation, lap shear, and static loading experiments. The unique combination of properties offered by LCE can lead to the development of roughness-tolerant adhesives, thereby broadening the application scope of PSAs.

Experimental Study on the Shear Behavior of HTRCS-Reinforced Concrete Beams

High-toughness resin concrete steel mesh (HTRCS) composites, as a novel reinforcement material, are extensively employed, yet there has been a lack of comprehensive quantitative studies on them, and our knowledge about them predominantly relies on experimental investigations. To delve into the shear performance of reinforced concrete beams fortified with HTRCS, this research executed four-point bending static load experiments on a benchmark of two standard beams and six HTRCS-reinforced beams. The results demonstrate that the shear bearing capacity of the reinforced concrete beams was notably enhanced with HTRCS, ranging from approximately 10% to 65%. Further examination revealed that the stiffness of the specimens is significantly influenced by the HTRCS thickness, shear–span ratio, and concrete strength, with the shear–span ratio exerting the most notable impact on stiffness. This analysis furnishes a solid theoretical foundation for the utilization of HTRCS.

Research on Strength of Bilateral Support Bearing of PDC–Cone Hybrid Bit

The existing PDC (polycrystalline diamond compact)–cone hybrid bit bearing adopts a unilateral support structure, which is prone to stress concentration in the journal area, resulting in fracture and wear failure of the bearing, thus reducing the service life of the hybrid bit. In this paper, a new type of double supported bearing hybrid bit is proposed. The static strength analysis of unilateral and bilateral support bearing structures is carried out by finite element simulation, and the stress and strain distribution of the two structures under loads of 20–100 kN is obtained. Experimental devices for unilateral and bilateral support bearing structures are designed and manufactured to complete 50–100 kN static pressure loading experiments. The results show that the stress and strain of unilateral and bilateral support bearing increased linearly with the increase of load. Compared with unilateral bearing, when the load was 100 kN, the maximum Mises stress of bilateral bearing decreased from 358.80 MPa to 211.10 MPa, with a decrease of 41.16%. The maximum contact stress decreased from 415.20 MPa to 378.10 MPa, a decreased of 8.94%, and the maximum principal strain decreased from 1.101 × 10−3 to 9.71 × 10−4, a decrease of 11.81%. The axial strain in the danger zone was reduced by 14.68% and 17.35%, respectively. It is found that the contact stress of the simulation data is highly correlated with the bearing life, and the service life of the bilateral bearing bit is increased by 8.94%. The simulation data and experimental results provide data support for the production of hybrid bits with bilateral bearing support.

Study on flexural behavior of concrete slabs strengthened with externally prestressed recycled bead wires

Recycled bead wires were prestressed for reinforced concrete slabs using an innovative anchor that our research group created. In this work, four concrete slab groups were designed: three reinforced groups and one control group. In this work, four concrete slab groups: three reinforced groups, and one control group were designed. The reinforced slabs were subjected to controlled stretching stress of 720 MPa, 900 MPa, and 1080 MPa. Four-point bending static load experiments were performed to verify the recommended reinforcement method and assess the effect of different controlled stretching stress on slab bending performance. This paper presents an analysis of the bearing capacity, crack behaviour, stiffness, and ductility of the specimens. The superior tensile and flexural capabilities of recycled bead wires were used as external prestressing reinforcement materials, as evidenced by the results. The reinforced slab exhibited a maximum increase in ultimate bearing capacity of 142 %, resulting in a significant enhancement of its flexural bearing capacity. The overall stiffness of the slab was successfully increased using recycled bead wires, and the fractures of the reinforced slab exhibited characteristics of fine and dense material. The 'inverted arch' effect of prestressed steel wires efficiently controlled the breadth of the fracture, postponed the onset of cracks, and decreased the degree of specimen damage. The application of more controlled stretching stress was associated with higher carrying capacity, and this also better restricted the development and expansion of cracks. A numerical simulation of four sets of concrete slabs was conducted using ABAQUS, with a subsequent comparative analysis of the results obtained with those of the experimental tests. Furthermore, the feasibility of this type of reinforcement was also confirmed by theoretical analyses of ultimate load-carrying capacity and cracking deflection. Their low-carbon qualities can address issues with waste resources and create new concepts for recycled waste tires.

Experimental evaluation and numerical investigation on the anti-collapse performance of beam-to-column connections in the minor-axis direction

This study examined the effects of structural resistance in both major- and minor-axis directions on the anti-collapse performance of a fully bolted composite frame. Current research in the field has focused predominantly on the anti-collapse performance of H-columns in the major-axis direction, potentially hindering accurate determination of anti-collapse transmission path within a structure. Herein, monotonic static loading experiments were conducted on two substructures in the minor-axis direction: one equipped with welded flange and bolted web connections and the other with fully bolted connections. The ductility development curve, dynamic collapse response curve, and resistance mechanism correlation curve were employed to evaluate the test results. Fully bolted connections exhibited superior nonlinear rotation capacity, which is essential for the development of a structure's catenary resistance The failure mechanisms and resistance development processes of the structures were reproduced using the ABAQUS/Explicit dynamic quasi-static modeling technique. A full-scale finite element model was developed for the frame with fully bolted connections loaded in the minor-axis direction. This research will contribute to the robust design of fully bolted structural frames that considers the effects of the column stiffness, thickness of the splicing cover plate, number of bolt rows, and bolt apertures of flange connections on deformation and resistance to loading in the minor-axis direction.

Carbon fiber reinforced composites with self‐sensing and self‐healing capabilities enabled by CNT‐modified nanofibers

AbstractCarbon fiber reinforced polymer (CFRP) composites with self‐sensing and self‐healing capabilities was developed in this work. Uniform dispersion of CNTs within a core‐shell nanofiber structure was achieved through a combination of electrospinning and subsequent surface spraying of CNTs. The resulting core‐shell nanofibers were incorporated into CFRP composites using a vacuum‐assisted resin transfer molding process. Mechanical testing demonstrated improved mechanical properties in the composites treated with CNT spraying. Real‐time, precise monitoring of structural damage was enabled through the measurement of electrical signal changes caused by composite deformation in static loading experiments. Furthermore, self‐healing experiments demonstrated that the thermally conductive network formed by CNTs facilitated more uniform heat transfer within the composites. During the healing process, resistive heating of damaged specimens was applied, resulting in a remarkable healing efficiency of 95.2%. The experiments indicate that the composite developed in this paper possess excellent self‐sensing and self‐healing capabilities.Highlights Damage self‐sensing and self‐healing CFRP composites were developed. CNTs‐modified nanofibers were applied to endow the composite specific abilities. Resistivity signals were collected for real‐time damage monitoring. The self‐healing efficiency of the designed composite reached up to 95.2%. Self‐sensing and self‐healing occurred autonomously within closed‐loop structure.

Moment Redistribution Effect of the Continuous Glass Fiber Reinforced Polymer-Concrete Composite Slabs Based on Static Loading Experiment

Moment Redistribution Effect of the Continuous Glass Fiber Reinforced Polymer-Concrete Composite Slabs Based on Static Loading Experiment

A sub-millinewton resolution biaxial force sensor with temperature self-compensation for vascular intervention

This article presents a fiber Bragg grating (FBG)-based highly sensitive micro-biaxial force sensor for vascular intervention surgery. It features a 3D-printed integrated structure incorporating an FBG- embedded cavity at its front end for temperature decoupling and an elliptical arc ball hinge to improve lateral sensitivity. Four FBG-embedded fibers are suspended in a circular array within the flexible hinge to minimize lateral strain crosstalk and increase measurement accuracy. Finite-element analysis has been implemented to validate the flexure performance, while both static and dynamic loading experiments have been performed to validate the sensor performance. The experiments revealed resolutions of 0.761 and 0.765 mN, respectively for the two lateral forces within a range of −1 to 1 N, and dynamic measurement error lower than 0.67 % of full scale. Temperature compensation experiments are conducted under loaded conditions for both axes, showing errors of lower than 1.6 % and 1.2 %. The ability to decouple force and temperature will benefit its broad application for vascular intervention surgery.

Structural stiffness and equivalent viscous damping in a supercritical carbon dioxide lubricated hybrid journal bearing under hydrostatic status

PurposeThe purpose of this paper is to propose a type of hybrid bearing lubricated with supercritical carbon dioxide (S-CO2) and to investigate the stiffness and damping characteristics of the bearing under hydrostatic status.Design/methodology/approachEstablished a test rig for radial bearings lubricated with S-CO2 and used it to measure the dynamic coefficients by recording the relative and absolute displacements of bearing. Test bearing is mounted on a nonrotating, stiff shaft. Using static loading experiments to obtain structural stiffness. The dynamic coefficient regularities of the test bearing under hydrostatic status were revealed through dynamic loading experiments.FindingsExperiment results indicate that test bearing displayed increased stiffness when subjected to high excitation frequencies and low excitation forces, as well as elevated damping when exposed to low excitation frequencies and low excitation forces. Additionally, an increase in either environmental pressure or hydrostatic recess pressure can elevate the dynamic coefficient. The effect of temperature on the dynamic coefficient is more pronounced around the critical temperature of S-CO2.Originality/valueDesigned a type of hybrid bearing for use in the Brayton cycle that is lubricated with S-CO2 and uses hydrostatic lubrication during start-stop and hydrodynamic lubrication during high-speed operation. The hybrid bearing reduces the wear and friction power consumption of gas bearing. However, few experimental analyses have been conducted by researchers in this field.

Experimental and numerical research on the static behavior of locally corroded OSBD

Corrosion can accelerate the deterioration of the mechanical properties of orthotropic steel bridge decks (OSBDs), seriously affecting the service safety of steel bridges. In this paper, thirty Q345C steel and four OSBD specimens with various corrosion levels are designed to investigate the effect of corrosion on the static behavior of OSBDs. Then, corrosion damage and its influence on mechanical properties are explored by static loading experiments. The constitutive model for Q345C steel is built considering the impact of corrosion. Finally, a numerical analysis considering geometric initial defects is employed to compare the effect of corrosion location on bearing capacity degradation. It is observed from the tested results that the corrosion led to the failure mode of Q345C steel changing from plastic failure to brittle failure. The ultimate bearing capacity of specimens with a local corrosion rate of 7.92%, 12.05%, and 16.24% decreased by 11.08%, 14.45%, and 17.82%, respectively. Corrosion leads to stress concentration in the top plate area, causing local instability of the structure. The degradation degree of the bearing capacity of the top plate is greater than that of the U-rib corrosion corresponding to the same corrosion conditions.

Experimental and finite element flexural performance study of HPEC beam

To improve the force-bearing performance and material utilization rate of steel-concrete composite structure and reduce the self-weight of the structure, a hollow-core partially-encased concrete composite (HPEC) beam was proposed. Four-point static loading experiments were performed on three HPEC beams and one fully-filled concrete composite beam to examine the bending damage mechanism and load-deflection curve of HPEC beams. The results show that the HPEC beams have more reasonable force-bearing performance under normal service conditions and can fully utilize the material properties than the fully filled concrete beams. Enhancing the concrete strength as well as increasing the concrete thickness would reduce the utilization of steel. To find out the factors which have the greatest impact on the bending performance of HPEC beams, the orthogonal test design was carried out by the finite element analysis software ABAQUS on the parameters of the HPEC beam such as section flange width, section flange thickness, web height, web thickness, and concrete filling thickness. The best parameter design solution was determined. The deflection formula of HPEC beams was derived based on the slip theory. The results of the deflection formula had an error of less than 8% compared with the test results, which verified the reasonableness of the formula.

The study on the characteristics of active force of neck muscles under rapid braking conditions

This paper studies the active force characteristics of the neck muscles under the condition of rapid braking, which can provide theoretical support for reducing the neck injury of pilots when carrier-based aircraft blocks the landing. We carried out static loading and real vehicle braking experiments under rapid braking conditions, collected the active contraction force and electromyography (EMG) signals of neck muscles, and analyzed the response characteristics of neck muscle active force response. The results showed that the head and neck forward tilt time was delayed and the amplitude decreased during neck muscle pre-tightening. The duration of the neck in the extreme position decreased, and the recovery towards the seat direction was faster. The EMG signals of trapezius muscle was higher than sternocleidomastoid muscle. This suggests that pilots can reduce neck injury by pre-tightening the neck muscles during actual braking flight. In addition, we can consider the design of relevant fittings for pre-tightening the neck muscles.

Fatigue fracture experiment of concrete members with cold joints under low stress and low stress amplitude fatigue load

Currently, numerous studies are conducted on the fatigue fracture performance of concrete, considering various factors such as material ratio, material content, and external environment. However, very few studies consider the impact of casting defects on the fatigue fracture performance of concrete. Cold joints, one of the typical casting defects, are weak joints caused by the discontinuous pouring of concrete structures. To investigate the fatigue fracture performance of concrete with cold joint defects, this study conducted fracture experiments using static load and interface nanoindentation experiments on 12 concrete experimental components with cold joints to analyze the fracture performance and cold joint interface characteristics. Subsequently, this study conducted fatigue fracture experiments on 144 experimental components with cold joints to analyze the fracture characteristics and fatigue life under low stress and low stress amplitude fatigue loads. The results indicate that the peak load, initiation fracture toughness, and unstable fracture toughness of concrete members with cold joints decrease with the extension of the pouring interval of cold joints. The thickness of the cold joint interface increases with the extension of the pouring interval, while the strength decreases with the extension of the pouring interval. The fatigue life of experimental components with cold joints reduces with stress and stress amplitude raising. Under the same initial stress and stress amplitude, the fatigue life of concrete members with cold joints decreases as the pouring interval extends, and the bearing performance deteriorates further after the same number of cyclic loading. Fatigue loads with low stress and low stress amplitudes can lead to the fatigue fracture of experimental components with cold joints. The research findings can serve as a foundation for the study of damage and cracking in lining with cold joints under aerodynamic fatigue loads in high-speed railway tunnels.

Failure characteristics and conditions of rock-coal combination structure with weak layer under dynamic and static stresses

To comprehensively understand the mechanical response of a rock-coal combination structure containing a weak layer, a series of laboratory static loading and impact loading experiments were conducted. The results showed that under static load, the sliding process of the rock coal structure was relatively slow, and fragments can be observed. Under the action of horizontal impact loading, the whole coal stratum slipped out rapidly, and the process lasted only 0.05 s. Under the horizontal and axial impact loads, the coal stratum remained stable first, and then it slipped out as a whole under the action of static load. Additionally, a sliding instability criterion of a rock coal structure containing a weak layer was established based on theoretical analysis. The key parameter P value was checked through a numerical simulation experiment. It was found that the value was linearly related to the mechanical properties of the weak layer and overburden stress, and the experimental results coincided with the theoretical results. Finally, the relationship between sliding rockburst and strain rockburst was discussed, and these results can provide an important scientific basis for the prevention and control of dynamic disasters in deep mining.

STRUCTURAL PERFORMANCE AND ULTIMATE STRENGTH EVALUATION OF PILE CAP FOR SINGLE PILE WITH HORIZONTAL TWO-WAY ECCENTRICITY

In this study, static loading experiments were conducted to study the structural performance of pile cap for single pile with horizontal two-way eccentricity and to establish its strength evaluation method. The results indicated that the maximum residual crack width and stresses of the reinforcements were lower than the limit values when the capacities of the specimens reached the allowable strengths. In addition, it was shown that the calculated results of the ultimate strength for each members using the bending analysis by the fiber model were showed good agreement with the maximum capacities of all specimens in this paper.

Invisible damage identification and danger warning for steel box girders using the metal magnetic memory method

Locating invisible damage and detecting the critical stress state leading to structural damage or failure are essential tasks in structural diagnosis. In this study, a four-point bending static loading experiment was conducted on two steel box girder members—one nondestructive, whereas the other had a butt weld—based on the metal magnetic memory (MMM) method. The correlation between the buckling failure position of the steel box girders and distribution characteristics of the magnetic signals was analyzed. The critical stress states of the elastic and elastic–plastic or elastic–plastic and plastic stages were statistically described using characteristic magnetic parameters. The results showed that the extremum position of the magnetic signal variationΔHpywell correlated with the location of the stress concentration. TheΔHpyextremum could locate the invisible damage position and predict the failure position, while the extremum of the average valueΔHpyaand integral value AofΔHpyvalue could accurately diagnose the critical stress state of steel box girders in the elastic and elastic–plastic or elastic–plastic and plastic stages. The proposed magnetic charge model could explain the distribution characteristics of the magnetic signals on the butt weld. These results are expected to provide a basis for effectively evaluating invisible damage using the MMM method.

A Study on the Structural Characteristics of the Blades of Wind Turbines under Static Load Condition

The study of the structural strength and stiffness of wind turbine blades is an important foundation and guarantee for analyzing the stability and reliability of the complete wind turbine. By analyzing the results of static load experiments and finite element calculation, the stress, strain and deflection of blades can be more precisely determined so as to assess the structural characteristics of blades. We conducted static load tests on the medium-size experimental blades developed by the Institute of Engineering Thermophysics, Chinese Academy of Sciences, and obtained the deflection conditions of flap-wise and edgewise bendings, as well as the analytic results on the strain of the main beams and trailing edges. Meanwhile, a finite element model of blades was built using ANSYS to analyze the maximum deformation, stress, and strain. The corresponding results were compared with those of static load experiments. Then the strain and bending properties of blades under the static load were investigated, and the characteristics of the safety application of blades were verified. The results show that: 1)Within the range of 100% design load, the deflection of edgewise and flapwise directions presented a linear relationship with the applied loads. 2) After the loads in the flapwise direction exceeded 100% design load, a non-linear relationship between the blade bending and the applied loads were found. 3)The blade beam and trailing edge retain good stiffness properties under big strain conditions, and the maximum deformation appeared at the maximum chord length of the trailing edge of the blades. Our results on the static load experiments were basically consistent with the finite element model simulation, which verified the accuracy of the results of the static load experiment and finite element simulation of blades.

A FBG pull-wire vertical displacement sensor for health monitoring of medium-small span bridges

With the increase of service life, a growing number of medium-small span bridges have suffered degradation and even serious damage, and the vertical displacement is one of the significant parameters for their safety condition and performance evaluation. In terms of medium-small span bridges, to solve the difficulty for long term vertical displacement measuring and the demand for low-cost monitoring, this paper proposes a fiber Bragg grating (FBG) pull-wire vertical displacement sensor, which owns advantages of low cost, high accuracy and convenient installation. Firstly, the calibration and temperature correction of the sensor were carried out. Secondly, the influences of the fixed angle and sag effect of the sensor on measuring results were investigated. Finally, the sensor was installed in an in-service hollow slab bridge and the static and dynamic load experiments were carried out. Results show that the linearity of the proposed sensor is 0.998, the sensitivity is 7.87 pm/mm, the hysteresis error is 1.54 %, the temperature correction coefficient is 18.08 pm/°C, the relative combined uncertainties are within 4 %; the fixed angle of this sensor is recommended to choose in the range of 15°-30° in order to obtain higher measuring accuracy; when θ = 15° and the radius of the external wire is 0.3 mm, the limit of the external wire length can be set to 19.5 m to avoid the influence of the wire sag effect on measuring results; the sensor is feasible in vertical displacement measurement of in-service medium-small span bridge, and the relative measuring errors in both static and dynamic load experiments are less than 5 %.

Prediction of the shear capacity of ultrahigh-performance concrete beams using neural network and genetic algorithm

Currently, concrete structures have increasingly higher requirements for the shear capacity of beams, and ultrahigh-performance concrete (UHPC) beams are increasingly widely used. To facilitate the design of UHPC beams, this paper constructs a UHPC beam shear strength prediction model. First, static shear tests were conducted on 6 UHPC beam specimens with a length of 2 m and a cross-sectional size of 200 mm × 300 mm to explore the effects of the UHPC strength, shear span ratio, hoop ratio, and steel fiber content on the shear resistance and failure morphology of the UHPC beams. Based on the results of this study and a static load experiment of 102 UHPC beams in the literature, the construction includes the shear span ratio (λ), beam section width (b), beam section height (h), hoop ratio (ρSV), UHPC compressive strength (fc), steel fiber volume fraction (Vf), and the UHPC beam shear capacity (Vex) 7 parameter database. Based on the construction of the database, 1200 BPNN models were trained through trial and error. The models were evaluated using the correlation coefficient R, root mean square error RMSE, and a20-index indicators, and the optimal BPNN model (6-15-8-1) was determined based on the ranking of RMSE. After the optimal BPNN is optimized by a genetic algorithm, the prediction performance of the model is improved. The correlation coefficient between the predicted value and the experimental value is R2 = 0.98667, and RMSE = 7.38. This model can reliably predict the shear strength of UHPC beams and provide designers with a reference for the design of UHPC beams. Finally, after sensitivity analysis, the influence of each input parameter on the UHPC shear capacity is determined.